This invention relates to wireless communication networks for voice and broadband data communication with fixed or mobile remote terminals.
Cellular communication systems providing mobile telephone service and other services have come into general use worldwide. These cellular systems divide geographical areas into small contiguous geographical cells. A base station is located within each cell for communication with users within that cell.
Since the cells are relatively small a very large number of cells must be provided to cover a large area. Extensive equipment must be provided at each cell base station, including mobile switching centers, base station controllers and base station transceivers. Thus, there is a need for expanded cell sizes to reduce the number of base station sites.
Current transmission systems generally employ low power directional antennas that are either omni-directional using one antenna or use several antennas to cover either two 180-degree or three 120-degree relatively short-range (3 to 7 km radius) sectors. Each sector has an inflexible fixed radiation pattern.
A user moving from one cell area to another during a voice or data transmission often experiences changes in signal level and quality. Interference between adjacent cells also can reduce signal quality. A cell base station service will suffer when an overly large number of users are active within that cell at one time. Adding sufficient equipment to handle very high traffic levels in every cell, even though traffic levels are normally low, is very expensive. Improvements in system handoff between cells and the ability to handle higher volume without maximizing resources in every cell are needed.
Attempts have been made to improve cell system efficiency by providing an antenna system forming number of narrow beams each covering a sector around the base station instead of an omnidirectional antenna, as described by Searle et al. in U.S. Pat. No. 5,596,329. While this arrangement has some advantages, it has problems with efficiently handling large differences in traffic between high and low usage periods.
Thus, there is a continuing need for improvements in cellular communications systems to greatly reduce the number of base station sites require to cover a specific geographic area, to reduce costs for infrastructure equipment and related service and operating costs, to permit reallocation of network resources to service peak busy periods, to permit easy and inexpensive expansion of a system as traffic increases, to minimize adjacent cell interference and to optimize handoff between cells.
The above-noted problems, and others, are overcome in accordance with this invention by a wireless communications network which basically comprises a plurality of transmit and receive antenna elements making up an antenna array, a plurality of amplifier modules corresponding to antenna array, a multiplexer in circuit-switched network (CSN) or a router in packet switched network (PSN) versions to combine and route the multiple circuit switched or packetized serial digital data streams to and from a central office and transceiver modem modules to convert an incoming, serial, digital data stream to a modulated radio frequency stream for transmission to a remote user (in one version the modem modules convert between digital and intermediate frequency and a second conversion modules converts between intermediate frequency and radio frequency). In most versions a switchable Butler matrix is preferably included to cause a beam of desired beamwidth to be radiated in accordance with a microprocessor-based controller. A receiver beam shaper/null steerer is preferably included to optimize the received beam shape for each channel to maximize received signal-to-noise ratio.
The transmission system of this invention uses a single site with variable and changeable on demand antenna radiation (beam) patterns. The radiation patterns are rendered changeable by the provision of multiple individual beams that typically vary in angular width from about 2 to 120 degrees. Each sector can support communications with multiple remote users with the number of simultaneous users per sector dependent on the International Communications Union standard employed (e.g., AMPS, GSM, CDMA, UMTS)
As the number of users within a given angular sector increases, in the system of this invention the beam size can be reduced by adding new beams, thus maintaining the number of users per beam. Similarly, as the number of users in a sector decreases, that sectors=users can be folded into adjacent sectors, thus reducing the number of active sectors. In this manner network resources are conserved and optimized to handle the diurnal changes in traffic patterns that naturally occur. Prior systems require the deployment of sufficient equipment to many sites to handle the peak hour traffic at each site without the ability to share network resources.
For optimum performance, minimum beamwidth is about 2 degrees. A 2-degree beamwidth for a uniformly weighted aperture requires a width of approximately 9.5 meters at 900 MHZ and 3.6 meters at 2.4 Ghz. A 25-30% larger aperture than the uniform aperture is preferred since sidelobe control is needed to maximize the number of simultaneous users per beam.
Each beam requires its own dedicated set of system resources; namely, transceivers, modems and antenna element feed network. Additionally, a number of system resources such as antenna elements, switching networks and controllers can be shared among beams. Each collection of antenna elements that form a beam covering a sector is driven by a suite of equipment that includes a switch path, modems, transmitters and receivers with the information that is being transported coming from external networks. With this novel system, there is a significant reduction in the system resources required, resulting in a substantial reduction in the cost of each base station transmission facility.
With the narrower beamwidths of this system and with the resulting higher antenna gains this system can provide reliable communications over a distance of 30 km or greater. The increased range capability significantly reduces the number of required base stations. This novel system will support both packet switched networks that are currently used to support data communications and circuit switched networks as are used to support the more traditional analog voice only wireless telephone networks.
A flexible call manager provides the interface between land-based communications systems and the radio frequency transmission system. The flexible call manager includes router and digital beam former elements in the packet switched embodiment and in the circuit switched embodiment is formed by the multiplexer and digital distribution network. Data coming to or from the antenna arrives either through a router (for packet switched network) or through a multiplexer (for a circuit switched network). Typically, packet switched network router traffic connects to the public switched telephone network through an H-323 gateway or directly to a packet switched network (e.g. the internet) while a circuit switched network multiplexer connects through a Class 5 switch to the public switched telephone network (PSTN).
Individual beams may be connected to a particular incoming PSTN source by the flexible call manager (i.e. the router and digital beam former elements). Since data being transmitted is in an internet protocol based format, in effect, each remote terminal has an internet protocol address. Each data stream (PSTN phone call, for example) is matched to a remote user by assignment of the remoter users internet protocol address. The flexible call manager provides this linkage and can provide an interface to user validation and network billing systems.